1. Technological Field
The disclosed technology relates to optical fluorescence-based, for example chemical and biochemical, sensors for example suitable for multi-analyte detection and to methods for fabricating such sensors.
2. Description of the Related Technology
Fluorescence-based gas sensors offer a high sensitivity and ease of operation. In addition, they offer the possibility of remote monitoring. Despite the availability of various schemes of fluorescence-based gas sensor platforms, a low-cost, flexible, compact and robust platform for multi-analyte detection still remains to be explored. In “Colorimetric gas sensors based on optical waveguides made on plastic foil,” Procedia Chemistry 1 (2009) 576-579, J. Courbat et al. report on the realization of a lowcost polymeric optical waveguide made on a plastic foil and used for colorimetric gas detection. The transducer concept is based on a planar optical waveguide made of a PET foil combined with surface mount device optical components (LEDs and photodiodes). Light coupling between the LEDs and the waveguide and between the waveguide and the photodiodes is realized by means of micromirrors formed on the PET foil. Gas sensing is based on the detection of variations in the light absorption in the evanescent field of a colorimetric film deposited on the plastic foil and sensitive to a specific gas to be detected. The light intensity that reaches the photodiode depends on the absorption of light in the evanescent field going along the colorimetric film. In this approach, the interaction of light with the sensing material is only through evanescent waves.
In “Development of an integrated optic oxygen sensor using a novel, generic platform,” Analyst (2005), 130(1): 41-45, C. S. Burke et al. describe the development of a generic platform for enhanced, integrated optic sensors based on fluorescence detection. The platform achieves enhanced performance and has inherent multi-analyte detection capability. The sensor chip comprises a ridge waveguide array on a planar substrate. Spots of fluorescent material sensitive to an analyte are deposited on one end of each waveguide and these spots are excited directly using a (non-integrated) LED source. The resulting fluorescence is coupled into the waveguides and propagates along their length to be detected at their respective endfaces by an appropriate detector. Direct excitation is an important design feature of the sensor chip as it is considerably more efficient than evanescent-wave excitation. In this approach the sensing area is limited, as it corresponds to the area of the fluorescent spots (having a diameter of e.g. 60 micrometer). Also, the output intensity distribution at the waveguide endface exhibits a strong angular peak, which dictates the optimal detector orientation out of the plane of the waveguide. This approach may be less suitable for fabricating integrated, planar sensors.